Method of manufacturing silver nanowires

ABSTRACT

A process for manufacturing silver nanowires is provided, wherein the recovered silver nanowires have a high aspect ratio; and, wherein the total glycol concentration is &lt;0.001 wt % at all times during the process.

This application claims priority to United States ProvisionalApplication No. 62/069,430 filed on Oct. 28, 2014.

The present invention relates generally to the field of manufacture ofsilver nanowires. In particular, the present invention is directed to amethod of manufacturing silver nanowires having a high aspect ratio foruse in various applications.

Films that exhibit a high conductivity in combination with a hightransparency are of great value for use as electrodes or coatings in awide range of electronic applications, including, for example, touchscreen displays and photovoltaic cells. Current technology for theseapplications involves the use of a tin doped indium oxide (ITO)containing films that are deposited through physical vapor depositionmethods. The high capital cost of physical vapor deposition processeshas led to the desire to find alternative transparent conductivematerials and coating approaches. The use of silver nanowires dispersedas a percolating network has emerged as a promising alternative to ITOcontaining films. The use of silver nanowires potentially offer theadvantage of being processable using roll to roll techniques. Hence,silver nanowires offer the advantage of low cost manufacturing with thepotential of providing higher transparency and conductivity thanconventional ITO containing films.

The “polyol process” has been disclosed for the manufacture of silvernanostructures. The polyol process uses ethylene glycol (or analternative glycol) as both a solvent and a reducing agent in theproduction of silver nanowires. The use of glycols; however, has severalinherent disadvantages. Specifically, using glycol as both the reducingagent and the solvent results in a decrease in control over the reactionas the principal reducing agent species (glycolaldehyde) is produced insitu and its presence and concentration are dependent on the extent ofexposure to oxygen. Also, the use of glycol introduces the potential forthe formation of combustible glycol/air mixtures in the headspace of thereactor used to produce the silver nanowires. Finally, the use of largevolumes of glycol create disposal concerns, increasing the cost ofcommercializing such operations.

One alternative approach to the polyol process for manufacturing silvernanowires has been disclosed by Miyagishima, et al. in United StatesPatent Application Publication No. 20100078197. Miyagishima, et al.disclose a method for producing metal nanowires, comprising: adding asolution of a metal complex to a water solvent containing at least ahalide and a reducing agent, and heating a resultant mixture at 150° C.or lower, wherein the metal nanowires comprise metal nanowires having adiameter of 50 nm or less and a major axis length of 5 μm or more in anamount of 50% by mass or more in terms of metal amount with respect tototal metal particles.

Another alternative approach to the polyol process for manufacturingsilver nanowires has been disclosed by Lunn, et al. in United StatesPatent Application Publication No. 20130283974. Lunn, et al. disclose aprocess for manufacturing high aspect ratio silver nanowires, whereinthe recovered silver nanowires exhibit an average diameter of 25 to 80nm and an average length of 10 to 100 μm; and, wherein the total glycolconcentration is <0.001 wt % at all times during the process.

Notwithstanding, there remains a need for alternative silver nanowiremanufacturing methods. In particular, for methods of manufacturingsilver nanowires without the use of glycol, wherein the silver nanowiresproduced have a high aspect ratio (preferably >500) and wherein theproduction of undesired silver nanoparticles having an aspect ratio of<3 is minimized.

The present invention provides a process for manufacturing high aspectratio silver nanowires, comprising: providing a container; providingwater; providing a reducing sugar; providing a polyvinyl pyrrolidone(PVP); providing a source of copper (II) ions; providing a source ofhalide ions; providing a source of silver ions; providing a pH adjustingagent; adding the water, the reducing sugar, the polyvinyl pyrrolidone(PVP), the source of copper (II) ions, the source of halide ions, andthe pH adjusting agent to the container to form a combination, whereinthe combination has a pH of 2.0 to 4.0; heating the combination to 110to 160° C.; then adding the source of silver ions to the container toform a growth mixture; then maintaining the growth mixture at 110 to160° C. for a hold period of 2 to 30 hours to provide a product mixture;and, recovering a plurality of high aspect ratio silver nanowires fromthe product mixture; and, wherein a total glycol concentration in thecontainer is <0.001 wt % at all times during the process.

The present invention provides a process for manufacturing high aspectratio silver nanowires, comprising: providing a container; providingwater; providing a reducing sugar; providing a polyvinyl pyrrolidone(PVP); providing a source of copper (II) ions; providing a source ofhalide ions; providing a source of silver ions; providing a pH adjustingagent; adding the water, the reducing sugar, the polyvinyl pyrrolidone(PVP), the source of copper (II) ions, the source of halide ions, andthe pH adjusting agent to the container to form a combination, whereinthe combination has a pH of 2.0 to 4.0; heating the combination to 110to 160° C.; then adding the source of silver ions to the container toform a growth mixture; maintaining the growth mixture at 110 to 160° C.for a hold period of 2 to 30 hours to provide a product mixture; and,recovering a plurality of high aspect ratio silver nanowires from theproduct mixture; wherein a total glycol concentration in the containeris <0.001 wt % at all times during the process; and, wherein theplurality of high aspect ratio silver nanowires recovered have anaverage diameter of 25 to 80 nm and an average length of 10 to 100 μm.

The present invention provides a process for manufacturing high aspectratio silver nanowires, comprising: providing a container; providingwater; providing a reducing sugar; providing a polyvinyl pyrrolidone(PVP); providing a source of copper (II) ions; providing a source ofhalide ions; providing a source of silver ions; providing a pH adjustingagent; adding the water, the reducing sugar, the polyvinyl pyrrolidone(PVP), the source of copper (II) ions, the source of halide ions, andthe pH adjusting agent to the container to form a combination, whereinthe combination has a pH of 2.0 to 4.0; dividing the source of silverions into a first portion and a second portion; heating the combinationto 140 to 160° C.; then adding the first portion to the container toform a creation mixture; then cooling the creation mixture to 110 to135° C. during a delay period; following the delay period, adding thesecond portion to the container to form a growth mixture; maintainingthe growth mixture at 110 to 160° C. for a hold period of 2 to 30 hoursto provide a product mixture; and, recovering a plurality of high aspectratio silver nanowires from the product mixture; and, wherein a totalglycol concentration in the container is <0.001 wt % at all times duringthe process.

The present invention provides a process for manufacturing high aspectratio silver nanowires, comprising: providing a container; providingwater; providing a reducing sugar; providing a polyvinyl pyrrolidone(PVP); providing a source of copper (II) ions; providing a source ofhalide ions; providing a source of silver ions; providing a pH adjustingagent; adding the water, the reducing sugar, the polyvinyl pyrrolidone(PVP), the source of copper (II) ions, the source of halide ions, andthe pH adjusting agent to the container to form a combination, whereinthe combination has a pH of 2.0 to 4.0; dividing the source of silverions into a first portion and a second portion; heating the combinationto 140 to 160° C., then adding the first portion to the container toform a creation mixture; then cooling the creation mixture to 110 to135° C. during a delay period; following the delay period, adding thesecond portion to the container to form a growth mixture; maintainingthe growth mixture at 110 to 135° C. for a hold period of 2 to 30 hours;and, recovering a plurality of high aspect ratio silver nanowires fromthe product mixture; wherein a total glycol concentration in thecontainer is <0.001 wt % at all times during the process.

The present invention provides a process for manufacturing high aspectratio silver nanowires, comprising: providing a container; providingwater; providing a reducing sugar, wherein the reducing sugar providedis glucose; providing a polyvinyl pyrrolidone (PVP), wherein thepolyvinyl pyrrolidone (PVP) provided has a weight average molecularweight, M_(W), of 40,000 to 60,000 Daltons; providing a source of copper(II) ions, wherein the source of copper (II) ions provided is copper(II) chloride; providing a source of halide ions, wherein the source ofhalide ions provided is sodium chloride; providing a source of silverions, wherein the source of silver ions provided is silver nitrate;providing a pH adjusting agent; adding the water, the reducing sugar,the polyvinyl pyrrolidone (PVP), the source of copper (II) ions, thesource of halide ions, and the pH adjusting agent to the container toform a combination, wherein the combination has a pH of 2.0 to 4.0;dividing the source of silver ions into a first portion and a secondportion; heating the combination to 140 to 160° C., then adding thefirst portion to the container to form a creation mixture; then coolingthe creation mixture to 110 to 135° C., during a delay period; followingthe delay period, adding the second portion to the container to form agrowth mixture; maintaining the growth mixture at 110 to 135° C. for ahold period of 2 to 30 hours; and, recovering a plurality of high aspectratio silver nanowires from the product mixture; wherein a total glycolconcentration in the container is <0.001 wt % at all times during theprocess.

The present invention provides a process for manufacturing high aspectratio silver nanowires, comprising: providing a container; providingwater; providing a reducing sugar, wherein the reducing sugar providedis D-glucose; providing a polyvinyl pyrrolidone (PVP), wherein thepolyvinyl pyrrolidone (PVP) provided has a weight average molecularweight, M_(W), of 40,000 to 60,000 Daltons; providing a source of copper(II) ions, wherein the source of copper (II) ions provided is copper(II) chloride; providing a source of halide ions, wherein the source ofhalide ions provided is sodium chloride; providing a source of silverions, wherein the source of silver ions provided is silver nitrate;providing a pH adjusting agent; adding the water, the reducing sugar,the polyvinyl pyrrolidone (PVP), the source of copper (II) ions, thesource of halide ions, and the pH adjusting agent to the container toform a combination, wherein the combination has a pH of 2.0 to 4.0;dividing the source of silver ions into a first portion and a secondportion, wherein the first portion is 10 to 30 wt % of the source ofsilver ions provided; heating the combination to 145 to 155° C., thenadding the first portion to the container to form a creation mixture;then cooling the creation mixture to 125 to 135° C. during a delayperiod of 5 to 15 minutes; following the delay period, adding the secondportion to the container to form a growth mixture; maintaining thegrowth mixture at 125 to 135° C. for a hold period of 16 to 20 hours;and, recovering a plurality of high aspect ratio silver nanowires fromthe product mixture; wherein a total glycol concentration in thecontainer is <0.001 wt % at all times during the process; wherein aweight ratio of polyvinyl pyrrolidone (PVP) to silver ions added to thecontainer is 6:1 to 7:1; wherein a weight ratio of halide ions to copper(II) ions added to the container is 2.5:1 to 3.5:1; wherein theplurality of high aspect ratio silver nanowires recovered have anaverage diameter of 35 to 50 nm and an average length of 40 to 100 μm;and, wherein the plurality of high aspect ratio silver nanowiresrecovered have an average aspect ratio of >500.

DETAILED DESCRIPTION

A process for manufacturing high aspect ratio silver nanowires has beenfound which provides silver nanowires having an average diameter of 25to 60 nm and an average length of 35 to 100 μm, while avoiding theinherent disadvantages associated with the use of glycols and while alsoreducing the fraction of silver nanoparticles produced having an aspectratio of <3. It is difficult to separate high aspect ratio silvernanowires from silver nanoparticles having an aspect ratio of <3.Accordingly, it is believed to be of significant benefit to have aprocess wherein the formation of silver nanoparticles produced having anaspect ratio of <3 is minimized such that the silver nanoparticlefraction, NP_(F), for the silver nanowires produced is <0.2 (asdetermined according the to method described herein in the Examples).

The term “total glycol concentration” as used herein and in the appendedclaims in reference to the container contents means combined total ofthe concentration of all glycols (e.g., ethylene glycol, propyleneglycol, butylene glycol, poly(ethylene glycol), poly(propylene glycol))present in the container.

The term “high aspect ratio” as used herein and in the appended claimsin reference to the recovered silver nanowires means that the averageaspect ratio of the recovered silver nanowires is >500.

The term “silver nanoparticle fraction” or “NP_(F)” used herein and inthe appended claims is the silver nanowire fraction of a sample ofsilver nanowires determined according to the following equation:NP_(F)=NP_(A) /T _(A)wherein T_(A) is the total surface area of a substrate that is occludedby a given deposited sample of silver nanowires; and, NP_(A) is theportion of the total occluded surface area that is attributable tosilver nanoparticles having an aspect ratio of <3 included in thedeposited sample of silver nanowires.

Preferably, the process for manufacturing high aspect ratio silvernanowires of the present invention, comprises: providing a container;providing water; providing a reducing sugar; providing a polyvinylpyrrolidone (PVP); providing a source of copper (II) ions; providing asource of halide ions; providing a source of silver ions; providing a pHadjusting agent; adding the water, the reducing sugar, the polyvinylpyrrolidone (PVP), the source of copper (II) ions, the source of halideions, and the pH adjusting agent to the container to form a combination,wherein the combination has a pH of 2.0 to 4.0 (preferably, of 2.2 to3.3); heating the combination to 110 to 160° C.; then adding the sourceof silver ions to the container (preferably with agitation) to form agrowth mixture; maintaining the growth mixture at 110 to 160° C. for ahold period of 2 to 30 hours to provide a product mixture; and,recovering a plurality of high aspect ratio silver nanowires from theproduct mixture; wherein a total glycol concentration in the containeris <0.001 wt % at all times during the process. Preferably, wherein aweight ratio of polyvinyl pyrrolidone (PVP) to silver ions added to thecontainer is 4:1 to 10:1; and, wherein a weight ratio of halide ions tocopper (II) ions added to the container is 1:1 to 5:1. Preferably,wherein the plurality of high aspect ratio silver nanowires recoveredhave an average diameter of 25 to 80 nm and an average length of 10 to100 μm. Preferably, wherein the plurality of high aspect ratio silvernanowires recovered have an average aspect ratio >500 (more preferably,≧800; most preferably, ≧1,000).

Preferably, the water provided in the process for manufacturing highaspect ratio silver nanowires of the present invention is at least oneof deionized and distilled to limit incidental impurities. Morepreferably, the water provided in the process for manufacturing highaspect ratio silver nanowires of the present invention is deionized anddistilled. Most preferably, the water provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention is ultrapure water that meets or exceeds the Type 1 waterrequirements according to ASTM D1193-99e1 (Standard Specification forReagent Water).

Preferably, the reducing sugar provided in the process for manufacturinghigh aspect ratio silver nanowires of the present invention is selectedfrom the group consisting of at least one of aldoses (e.g., glucose,glyceraldehyde, galactose, mannose); disaccharides with a freehemiacetal unit (e.g., lactose and maltose); and ketone bearing sugars(e.g., fructose). More preferably, the reducing sugar provided in theprocess for manufacturing high aspect ratio silver nanowires of thepresent invention is selected from the group consisting of at least oneof an aldose, lactose, maltose and fructose. Still more preferably, thereducing sugar provided in the process for manufacturing high aspectratio silver nanowires of the present invention is selected from thegroup consisting of at least one of glucose, glyceraldehyde, galactose,mannose, lactose, fructose and maltose. Most preferably, the reducingsugar provided in the process for manufacturing high aspect ratio silvernanowires of the present invention is D-glucose.

Preferably, the polyvinyl pyrrolidone (PVP) provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention has a weight average molecular weight, M_(W), of 20,000 to300,000 Daltons. More preferably, the polyvinyl pyrrolidone (PVP)provided in the process for manufacturing high aspect ratio silvernanowires of the present invention has a weight average molecularweight, M_(W), of 30,000 to 200,000 Daltons. Most preferably, thepolyvinyl pyrrolidone (PVP) provided in the process for manufacturinghigh aspect ratio silver nanowires of the present invention has a weightaverage molecular weight, M_(W), of 40,000 to 60,000 Daltons.

Preferably, the source of copper (II) ions provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention is selected from the group consisting of at least one of CuCl₂and Cu(NO₃)₂. More preferably, the source of copper (II) ions providedin the process for manufacturing high aspect ratio silver nanowires ofthe present invention is selected from the group consisting of CuCl₂ andCu(NO₃)₂. Most preferably, the source of copper (II) ions provided inthe process for manufacturing high aspect ratio silver nanowires of thepresent invention is CuCl₂, wherein the CuCl₂ is a copper (II) chloridedihydrate.

Preferably, the source of halide ions provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention is selected from the group consisting of at least one of asource of chloride ions, a source of fluoride ions, a source of bromideions and a source of iodide ions. More preferably, the source of halideions provided in the process for manufacturing high aspect ratio silvernanowires of the present invention is selected from the group consistingof at least one of a source of chloride ions and a source of fluorideions. Still more preferably, the source of halide ions provided in theprocess for manufacturing high aspect ratio silver nanowires of thepresent invention is a source of chloride ions. Most preferably, thesource of halide ions provided in the process for manufacturing highaspect ratio silver nanowires of the present invention is a source ofchloride ions, wherein the source of chloride ions is an alkali metalchloride. Preferably, the alkali metal chloride is selected from thegroup consisting of at least one of sodium chloride, potassium chlorideand lithium chloride. More preferably, the alkali metal chloride isselected from the group consisting of at least one of sodium chlorideand potassium chloride. Most preferably, the alkali metal chloride issodium chloride.

Preferably, the source of silver ions provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention is a silver complex. More Preferably, the source of silverions provided in the process for manufacturing high aspect ratio silvernanowires of the present invention is a silver complex; wherein thesilver complex is selected from the group consisting of at least one ofsilver nitrate (AgNO₃) and silver acetate (AgC₂H₃O₂). Most preferably,the source of silver ions provided in the process for manufacturing highaspect ratio silver nanowires of the present invention is silver nitrate(AgNO₃). Preferably, the source of silver ions provided in the methodfor manufacturing high aspect ratio silver nanowires of the presentinvention has a silver concentration of 0.005 to 1 molar (M)(morepreferably, of 0.01 to 1 M; most preferably, of 0.4 to 1 M).

Preferably, the pH adjusting agent provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention is an acid. More preferably, the pH adjusting agent providedin the process for manufacturing high aspect ratio silver nanowires ofthe present invention is an acid, wherein the acid is selected from thegroup consisting of at least one of inorganic acids (e.g., nitric acid,sulfuric acid, hydrochloric acid, fluorosulfuric acid, phosphoric acid,fluoroantimonic acid) and organic acids (e.g., methane sulfonic acid,ethane sulfonic acid, benzene sulfonic acid, acetic acid, fluoroaceticacid, chloroacetic acid, citric acid, gluconic acid, lactic acid).Preferably, the pH adjusted agent provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention has a pH of <2.0. Still more preferably, the pH adjustingagent provided in the process for manufacturing high aspect ratio silvernanowires of the present invention includes nitric acid. Mostpreferably, the pH adjusting agent provided in the process formanufacturing high aspect ratio silver nanowires of the presentinvention is aqueous nitric acid.

Preferably, in the process for manufacturing high aspect ratio silvernanowires of the present invention, the water, the reducing sugar, thepolyvinyl pyrrolidone (PVP), the source of copper (II) ions, the sourceof halide ions and the pH adjusting agent are added to a container(preferably, wherein the container is a reactor; more preferably,wherein the container is a reactor outfitted with an agitator) to form acombination; and then, the source of silver ions are added to thecombination in the container (preferably, with agitation) to form agrowth mixture while maintaining the combination at 110 to 160° C.(preferably, 125 to 155° C.; more preferably, 130 to 150° C.) duringaddition of the source of silver ions and after addition of the sourceof silver ions for a hold period of 2 to 30 hours (preferably, 4 to 30hours; more preferably 10 to 25 hours; most preferably, 16 to 20 hours)to provide the product mixture.

Preferably, the water, the reducing sugar, the polyvinyl pyrrolidone(PVP), the source of copper (II) ions, the source of halide ions and thepH adjusting agent are added to the container in any order in individualsequence (i.e., one at a time), simultaneously (i.e., all at the sametime), or semi-simultaneously (i.e., some individually one at a time,some simultaneously at the same time or as subcombinations). Morepreferably, at least two of the water, the reducing sugar, the polyvinylpyrrolidone (PVP), the source of copper (II) ions, the source of halideions and the pH adjusting agent are mixed together to form asubcombination before addition to the container.

Preferably, the water is divided into at least two volumes of water(more preferably, at least three volumes of water; most preferably, atleast four volumes of water) to facilitate the formation of at least twosubcombinations that include water before addition to the container.More preferably, the water is divided into at least four volumes ofwater, wherein a first volume of water is combined with the reducingsugar and the polyvinyl pyrrolidone (PVP) to form a reducing sugar/PVPsubcombination, wherein a second volume of water is combined with thesource of copper (II) ions to form a copper (II) ion subcombination,wherein a third volume of water is combined with the source of halideions to form a halide ion subcombination and wherein a forth volume ofwater is combined with the source of silver ions to form a silver ionsubcombination. Preferably, the reducing sugar/PVP subcombination, thecopper (II) ion subcombination, the halide ion subcombination and the pHadjusting agent are added to the container in any order in individualsequence (i.e., one at a time), simultaneously (i.e., all at the sametime), or semi-simultaneously (i.e., some individually one at a time,some simultaneously at the same time or as further subcombinations) toform the combination. More preferably, the reducing sugar/polyvinylpyrrolidone (PVP) subcombination is added to the container, followed bythe addition to the container of the copper (II) ion subcombination, thehalide ion subcombination and the pH adjusting agent in any order inindividual sequence (i.e., one at a time), simultaneously (i.e., all atthe same time), or semi-simultaneously (i.e., some individually one at atime, some simultaneously at the same time or as furthersubcombinations) to form the combination. Most preferably, the reducingsugar/polyvinyl pyrrolidone (PVP) subcombination is added to thecontainer, followed by the addition of the copper (II) ionsubcombination to the container, followed by the addition of the halideion subcombination to the container, followed by the addition of the pHadjusting agent to the container to form the combination. The silver ionsubcombination is then added to the combination in the container.

Preferably, in the process for manufacturing high aspect ratio silvernanowires of the present invention, a total glycol concentration in thecontainer is <0.001 wt % at all times during the process.

Preferably, in the process for manufacturing high aspect ratio silvernanowires of the present invention, the weight ratio of polyvinylpyrrolidone (PVP) to silver added to the container is 4:1 to 10:1 (morepreferably, 5:1 to 8:1; most preferably, 6:1 to 7:1).

Preferably, in the process for manufacturing high aspect ratio silvernanowires of the present invention, the weight ratio of halide ions tothe copper (II) ions added to the container is 1:1 to 5:1 (morepreferably, 2:1 to 4:1; most preferably, 2.5:1 to 3.5:1).

Preferably, in the process for manufacturing high aspect ratio silvernanowires of the present invention, the plurality of high aspect ratiosilver nanowires recovered from the product mixture have an averagediameter of 25 to 80 nm (more preferably, 25 to 60 nm; most preferably,35 to 50 nm) and an average length of 10 to 100 μm (preferably, 20 to100 μm; more preferably, >20 to 100 μm). Preferably, the plurality ofhigh aspect ratio silver nanowires recovered from the product mixturehave an average aspect ratio of >500.

Preferably, in the process for manufacturing high aspect ratio silvernanowires of the present invention, the plurality of high aspect ratiosilver nanowires recovered from the product mixture have a silvernanoparticle fraction, NP_(F), of <0.2 (preferably, <0.17; morepreferably, <0.15; most preferably, <0.13) (as determined according theto method described herein in the Examples).

Preferably, the process for manufacturing high aspect ratio silvernanowires of the present invention, further comprises: dividing thesource of silver ions provided into at least two individual portions,wherein the individual portions are added to the container with a delayperiod (preferably, of 1 to 60 minutes; more preferably, of 1 to 20minutes; most preferably of 5 to 15 minutes) between the individualportion additions. More preferably, the method of the present inventionfurther comprises: dividing the source of silver ions provided into afirst portion and a second portion (preferably, wherein the firstportion is 10 to 30 wt % of the source of silver ions provided; morepreferably, wherein the first portion is 15 to 25 wt % of the source ofsilver ions provided; most preferably, wherein the first portion is 20wt % of the source of silver ions provided); heating the combination to140 to 160° C. (preferably, 145 to 155° C.) before adding the firstportion to the container to form a creation mixture; and then coolingthe creation mixture to 110 to 150° C. (preferably, 110 to 135° C.; morepreferably, 125 to 135° C.) during a delay period (preferably, of 1 to60 minutes; more preferably, of 1 to 20 minutes; most preferably, of 5to 15 minutes); following the delay period, adding the second portion tothe container to form a growth mixture.

Preferably, the process for manufacturing high aspect ratio silvernanowires of the present invention, further comprises: dividing thesource of silver ions provided into a first portion and a second portion(preferably, wherein the first portion is 10 to 30 wt % of the source ofsilver ions provided; more preferably, wherein the first portion is 15to 25 wt % of the source of silver ions provided; most preferably,wherein the first portion is 20 wt % of the source of silver ionsprovided); heating the combination to 140 to 160° C. (preferably, 145 to155° C.) before adding the first portion to the container to form acreation mixture; then cooling the creation mixture to 110 to 150° C.(preferably, 110 to 135° C.; more preferably, 125 to 135° C.) during adelay period (preferably, of 1 to 60 minutes; more preferably, of 1 to20 minutes; most preferably, of 5 to 15 minutes); following the delayperiod, adding the second portion to the container to form a growthmixture; and, maintaining the growth mixture at 110 to 150° C.(preferably, 110 to 135° C.; more preferably, 125 to 135° C.) for a holdperiod of 2 to 30 hours (preferably, 4 to 30 hours; more preferably 10to 25 hours; most preferably, 16 to 20 hours) to provide a productmixture.

Some embodiments of the present invention will now be described indetail in the following Examples.

The water used in the following Examples was obtained using aThermoScientific Barnstead NANOPure purification system with a 0.2 μmpore size hollow fiber filter positioned downstream of the waterpurification unit.

Example 1: Preparation of Reducing Sugar/PVP Containing Subcombination

Polyvinyl pyrrolidone (PVP) having a weight average molecular weight,M_(W), of 55,000 Daltons (52.2 g; >98% from Sigma-Aldrich) was dissolvedin 1,958 mL of deionized water in a flask. Then D-glucose (13.5 g; >99%from Sigma-Aldrich) was added to the contents of the flask with stirringuntil dissolved to form a reducing sugar/PVP subcombination.

Example 2: Preparation of Copper (II) Ion Containing Subcombination

Copper (II) chloride (0.6137 g; >99% from Mallinckrodt Chemicals) wasdissolved in 900 mL of deionized water to form a copper (II) ionsubcombination in a beaker.

Example 3: Preparation of Halide Ion Containing Subcombination

Sodium chloride (0.2104 g) was dissolved in 900 mL of deionized water toform a halide ion subcombination in a beaker.

Example 4: Preparation of Silver Ion Containing Subcombination

Silver nitrate (12.70 g; >99% from Sigma-Aldrich) was dissolved in 612mL of deionized water to form a silver ion subcombination in a flask.

Comparative Example C1: Preparation of Silver Nanowires

An 8 L stainless steel pressure reactor outfitted with an overhead mixerand a temperature controller was used. A portion (21.3 mL) of a halideion subcombination prepared according to Example 3 was added to areducing sugar/PVP subcombination prepared according to Example 1 in aflask. A portion (21.3 mL) of a copper (II) ion subcombination preparedaccording to Example 2 was then added to the flask. The glassware usedin the measurement of the halide ion subcombination and the copper (II)ion subcombination was then rinsed with deionized water (407 mL) intothe flask. The contents of the flask were then transferred to thereactor. The flask was then rinsed with deionized water (191 mL) intothe reactor. The pH of the reactor contents was observed to be 3.86. Themixer was engaged at a stirring rate of 200 revolutions per minute. Thereactor was then closed up and purged with nitrogen 4 times to apressure of >60 psig with a hold at pressure for three minutes for eachpurge. The reactor was left with a nitrogen blanket at 16.8 psigfollowing the final purge. The temperature controller was then set at150° C. After the reactor contents reached 150° C., 20 wt % of thesilver ion subcombination prepared according to Example 4 was added tothe reactor over 1 minute. The reactor contents were then stirred forten minutes while maintaining the set point of the temperaturecontroller at 150° C. Over the following ten minutes, the temperature ofthe reactor contents was cooled down to 130° C. The remaining 80 wt % ofthe silver ion subcombination prepared according to Example 4 was thenadded to the reactor contents over the next ten minutes along with anadditional 102 mL of deionized water. The reactor contents were thenstirred for eighteen hours while maintaining the set point of thetemperature controller at 130° C. The reactor contents were then cooleddown to room temperature over the next thirty minutes. The reactor wasthen vented to relieve and pressure build up in the vessel. The mixerwas disengaged. The reactor contents were then collected.

Example 5: Preparation of Silver Nanowires

An 8 liter stainless steel pressure reactor outfitted with a three bladepropeller style agitator, a temperature control unit with an externalresistive heating mantle and an internal cooling tube to facilitatetemperature control was used. A portion (21.3 mL) of a halide ionsubcombination prepared according to Example 3 was added to a reducingsugar/PVP subcombination prepared according to Example 1 in a flask. Aportion (21.3 mL) of a copper (II) ion subcombination prepared accordingto Example 2 was then added to the flask. The glassware used in themeasurement of the halide ion subcombination and the copper (II) ionsubcombination was then rinsed with deionized water (407 mL) into theflask. The pH of the contents of the flask was then adjusted from aninitial pH of 3.86 down to a pH of 2.29 with nitric acid (ACS reagentgrade 70%). The contents of the flask were then transferred to thereactor. The flask was then rinsed with deionized water (191 mL) intothe reactor. The mixer was engaged at a stirring rate of 200 revolutionsper minute. The reactor was then closed up and purged with nitrogen 4times to a pressure of >60 psig with a hold at pressure for threeminutes for each purge. The reactor was left with a nitrogen blanket at16.8 psig following the final purge. The temperature controller was thenset at 150° C. After the reactor contents reached 150° C., 20 wt % ofthe silver ion subcombination prepared according to Example 4 was addedto the reactor over 1 minute to form a creation mixture. The creationmixture was then stirred for ten minutes while maintaining the set pointof the temperature controller at 150° C. Over the following ten minutes,the set point of the temperature controller was linearly ramped down to130° C. The remaining 80 wt % of the silver ion subcombination preparedaccording to Example 4 was then added to the reactor over the next tenminutes along with an additional 102 mL of deionized water to form agrowth mixture. The growth mixture was then stirred for eighteen hourswhile maintaining the set point of the temperature controller at 130° C.to form a product mixture. The product mixture was then cooled down toroom temperature over the next thirty minutes. The reactor was thenvented to relieve any pressure build up in the vessel. The mixer wasdisengaged. The product mixture was then collected.

Recovered Silver Nanowire Analysis

The product silver nanowires from Comparative Example C1 and Example 5were then analyzed using an FEI Nova NanoSEM field emission gun scanningelectron microscope (SEM) using FEI's Automated Image Acquisition (AIA)program. A drop of cleaned dispersion was taken from the UV/Vis cuvetteand drop-cast onto a silica wafer coated SEM stub before being driedunder vacuum. Backscatter electron images were collected using an FEINova NanoSEM field emission gun scanning electron microscope. FEI'sAutomated Image Acquisition (AIA) program was used to move the stage,focus, and collect images. Eighteen images of each sample were acquiredat 6 μm horizontal field width. Semi-automated image analysis usingImageJ software categorized objects as wires versus particles based onan aspect ratio of 3. Wire widths were automatically measured as well asthe total area of wires in the images. Particles were tabulated forindividual size and total area of particles in the images. ImageJsoftware was also used to determine the silver nanowire diameter inTABLE 1. The average length of the silver nanowires was observed toexceed 20 μm, based on the SEM images obtained for the diameteranalysis.

ImageJ software was used to analyze SEM images of the product silvernanowires from each of Comparative Example C1 and Example 5 to provide arelative measure of the silver nanoparticles having an aspect ratio of<3 in the product samples. The statistic used for this measure is thenanoparticle fraction, NP_(F), determined according to the followingexpression:NP_(F)=NP_(A) /T _(A);wherein T_(A) is the total surface area of the substrate that isoccluded by a given deposited sample of silver nanowires; and, NP_(A) isthe portion of the total occluded surface area that is attributable tosilver nanoparticles having an aspect ratio of <3.

Spectral UV/Vis analysis of the product silver nanowires from each ofComparative Example C1 and Example 5 was performed using a Shimadzu UV2401 Spectrophotometer. The raw UV/Vis absorbance spectra werenormalized so that the local minimum near 320 nm and the local maximumnear 375 nm span the range from 0 to 1. The wavelength of maximumabsorbance, λ_(max), and the normalized absorbance at 500 nm, Abs₅₀₀,are reported in TABLE 1.

TABLE 1 Spectral Width (nm) Analysis Standard λ_(max) Example MedianMean Deviation NP_(F) nm Abs₅₀₀ C1 44.6 53.7 33.4 0.23 380 0.39 5 38.247.8 35.2 0.12 378 0.27

We claim:
 1. A process for manufacturing high aspect ratio silver nanowires, comprising: providing a container; providing water; providing a reducing sugar; providing a polyvinyl pyrrolidone (PVP); providing a source of copper (II) ions; providing a source of halide ions; providing a source of silver ions; providing a pH adjusting agent; adding the water, the reducing sugar, the polyvinyl pyrrolidone (PVP), the source of copper (II) ions, the source of halide ions, and the pH adjusting agent to the container to form a combination, wherein the combination has a pH of 2.0 to 4.0; heating the combination to 110 to 160° C.; then adding the source of silver ions to the container to form a growth mixture; then maintaining the growth mixture at 110 to 160° C. for a hold period of 2 to 30 hours to provide a product mixture; and, recovering a plurality of high aspect ratio silver nanowires from the product mixture; and, wherein a total glycol concentration in the container is <0.001 wt % at all times during the process.
 2. The process of claim 1, further comprising: dividing the source of silver ions into a first portion and a second portion; heating the combination to 140 to 160° C.; then adding the first portion to the container to form a creation mixture; then cooling the creation mixture to 110 to 135° C. during a delay period; following the delay period, adding the second portion to the container to form the growth mixture.
 3. The process of claim 2, wherein the growth mixture is maintained at 110 to 135° C. during the hold period.
 4. The process of claim 3, wherein the reducing sugar provided is glucose.
 5. The process of claim 3, wherein the polyvinyl pyrrolidone (PVP) provided has a weight average molecular weight, M_(W), of 40,000 to 150,000 Daltons.
 6. The process of claim 3, wherein the source of copper (II) ions provided is copper (II) chloride.
 7. The process of claim 3, wherein the source of halide ions provided is sodium chloride.
 8. The process of claim 3, wherein the source of silver ions provided is silver nitrate.
 9. The process of claim 1, further comprising: dividing the source of silver ions into a first portion and a second portion; heating the combination to 140 to 160° C.; then adding the first portion to the container to form a creation mixture; then cooling the creation mixture to 110 to 135° C. during a delay period; following the delay period, adding the second portion to the container to form the growth mixture; and, maintaining the growth mixture at 110 to 135° C. during the hold period; wherein the reducing sugar provided is glucose; wherein the polyvinyl pyrrolidone (PVP) provided has a weight average molecular weight, M_(W), of 40,000 to 60,000 Daltons; wherein the source of copper (II) ions provided is copper (II) chloride; wherein the source of halide ions provided is sodium chloride; and, wherein the source of silver ions provided is silver nitrate.
 10. The process of claim 1, further comprising: dividing the source of silver ions into a first portion and a second portion, wherein the first portion is 10 to 30 wt % of the source of silver ions provided; heating the combination to 145 to 155° C.; then adding the first portion to the container to form a creation mixture; then cooling the creation mixture to 125 to 135° C. during a delay period of 5 to 15 minutes; following the delay period, adding the second portion to the container to form the growth mixture; and, maintaining the growth mixture at 125 to 135° C. during the hold period, wherein the hold period is 16 to 20 hours; wherein the reducing sugar provided is D-glucose; wherein the polyvinyl pyrrolidone (PVP) provided has a weight average molecular weight, M_(W), of 40,000 to 60,000 Daltons; wherein the source of copper (II) ions provided is copper (II) chloride; wherein the source of halide ions provided is sodium chloride; wherein the source of silver ions provided is silver nitrate; and, wherein a weight ratio of polyvinyl pyrrolidone (PVP) to silver ions added to the container is 6:1 to 7:1; wherein a weight ratio of halide ions to copper (II) added to the container is 2.5:1 to 3.5:1; wherein the plurality of high aspect ratio silver nanowires recovered have an average diameter of 35 to 50 nm and an average length of 20 to 100 μm; and, wherein the plurality of high aspect ratio silver nanowires recovered have an average aspect ratio of >500. 